Currently, there are several methods and devices that provide tracking of mobile devices. The tracking may provide real-time positioning of a device in an outside environment. For example, the device and its user may be located by using a device that has an assisted global positioning system (AGPS) or a device that uses a tri-angulation/tri-lateration method. The device may be a standalone GPS system, or a tracking system may be integrated in a mobile station, personal digital assistant (PDA), portable computer, etc. For discussion purposes and throughout the specification, it is assumed that the “device” is a mobile station, but is not limited thereto.
In an indoor environment, such as a large office building, locating a mobile station is more difficult, because location signals, e.g., GPS signals, may not be received by a mobile station. Further, if cellular coverage inside the building is provided by outdoor base stations, the complex propagation environment of the building reduces the accuracy of the triangulation or tri-lateration method. In addition, if the cellular coverage inside the building is provided by a distributed antenna system (DAS), the delay in the DAS system may distort the results of the triangulation or tri-lateration method, causing significant inaccuracy.